1. Field of the Invention
The present invention relates to a fuel cell stack in which electrolyte electrode assemblies and separators are stacked in a horizontal direction. Each of the electrolyte electrode assemblies includes a pair of electrodes and an electrolyte interposed between the electrodes.
2. Description of the Related Art
For example, a solid polymer electrolyte fuel cell employs an electrolyte membrane (electrolyte). The electrolyte membrane is a polymer ion exchange membrane. The electrolyte membrane is interposed between an anode and a cathode to form a membrane electrode assembly (MEA). The membrane electrode assembly is sandwiched between a pair of separators to form a unit cell for generating electricity. The fuel cell normally is used in the form of a fuel cell stack, by stacking a predetermined number of unit cells.
In the fuel cell, a fuel gas flow field is formed in a surface of one separator facing the anode for supplying a fuel gas to the anode, and an oxygen-containing gas flow field is formed in a surface of the other separator facing the cathode for supplying an oxygen-containing gas to the cathode. Further, a coolant flow field is formed between the separators for supplying a coolant along surfaces of the separators.
Furthermore, it is frequently the case that in the interior of the fuel cell, there are provided a fuel gas supply passage and a fuel gas discharge passage through which the fuel gas flows, an oxygen-containing gas supply passage and an oxygen-containing gas discharge passage through which the oxygen-containing gas flows, and a coolant supply passage and a coolant discharge passage through which the coolant flows, each of which extends through the fuel cell in the stacking direction of the unit cells so as to provide a so-called internal manifold type of fuel cell.
As technology concerning internal manifold type fuel cells, Japanese Laid-Open Patent Publication 2000-260439 is known. Such a fuel cell, as shown in FIG. 19, includes a spacer 1 for assuring passage of the coolant. In a peripheral portion 2 of the spacer 1, passages 3 forming one reactant gas flow passage and passages 4 forming another reactant gas flow passage are provided in a vertical direction. On opposite sides in the vertical direction of the peripheral portion 2, respective pairs of passages 5 forming coolant passages are provided. The passages 5 communicate with a central coolant space 7 via connecting passages 6.
Incidentally, with such a fuel cell, during assembly thereof or when performing maintenance thereon, an operation is carried out in order to fill the coolant into the interior of the fuel cell. However, with the aforementioned spacer 1, at upper parts of each of the passages 5 disposed at lower portions on both sides of the peripheral portion 2, opening parts 8 exist, which are separated upwardly from the connecting passages 6. Consequently, it is easy for air to become trapped and retained in the opening parts 8, and such air cannot be extracted (i.e., vented).
Further, in Japanese Laid-Open Patent Publication 2000-260439, as shown in FIG. 20, a separator 1a made from stainless steel is provided, in which a flow field (grooves) 2a for the coolant is formed, for example, by adopting a corrugated (wavelike) plate structure therein.
Opposite ends of grooves 2a are connected via groove contacting portions 3a, whereby passages are assured which enable the coolant to traverse through the grooves 2a. At opposite edges of the separator 1a, passages 4a are formed, which make up coolant passages, and which constitute pathways for carrying out supply and discharge of the coolant.
Non-illustrated spacers are stacked on the separator 1a. Passages for guiding the coolant into the groove contacting portions 3a of the separator 1a are formed in a peripheral portion of the spacers.
However, after the coolant has been introduced into the groove contacting portions 3a from passages that are formed in the periphery of the spacers, the coolant is supplied in a straight line along the grooves 2a that communicate with the groove contacting portions 3a. Owing thereto, specialized spacers must be used. Such spacers increase the number of parts required from the fuel cell, the fuel cell overall has an increased dimension in the stacking direction, and costs for the fuel cell are increased.